1. Field of the Invention
The present invention relates generally to disk drive spindle motors, and more particularly to a spindle motor having inner and outer ball bearing sets.
2. Description of the Prior Art
The typical hard disk drive includes a disk drive base, and a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to the disk drive base. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA) that includes at least one transducer head, typically several, for reading and writing data from the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The heads stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The spindle motor typically includes a spindle motor base, a central shaft, a rotatable hub, a stator, a magnet attached to the hub, and vertically spaced upper and lower ball bearing sets mounted upon the central shaft which facilitate rotational attachment of the hub to the spindle motor base. Each ball bearing set includes inner and outer ball bearing races which encase a plurality of ball bearings. The inner ball bearing races engage the central shaft and the outer ball bearing races engage the hub. This configuration allows for rotational movement of the outer ball bearing races relative to the inner ball bearing races for rotation of the hub. The hub further includes an outer flange which is used to support one or more of the disks. The upper and lower ball bearing sets are pre-loaded in compression to maintain the hub, and the disks supported on the hub, in an orthogonal configuration with respect to the shaft. The stator includes a series of coils and is concentrically positioned about the shaft, adjacent the hub. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet otherwise associated with the hub, thereby imparting a rotational motion onto the hub. Rotation of the hub results in the rotation of the attached disks.
A topic of concern is the desire to reduce the overall disk drive size. Such disk drives may have a variety of applications such as in hand held or portable electronic devices. The exterior size and shape of the disk drive is often referred to as a xe2x80x9cform factorxe2x80x9d. Reduction of such disk drive form factor has proven challenging. This is because the mere reduction of the size of the various disk drive components may result in such components being unable to conform to required specifications and standard form factors for such components, and may result in installation or assembly difficulties. As such reduced sized disk drives may have applications in hand held or mobile electronic device, the specifications may be even be tighter as compared to personal computer applications. For example, those specifications related to susceptibility to damage resulting from shock.
One particular area of focus is the reduction of the height of the spindle motor. In a typical configuration, the spindle motor height may be a function of the upper and lower ball bearing set arrangement. The mere reduction of the sizing of the upper and lower ball bearing sets impacts the susceptibility to damage resulting from shock, potential use of non-standard form factor bearing sets, and difficulties in conforming to allotted space requirements for such bearings. Accordingly, there is a need in the art for an improved spindle motor ball bearing configuration in comparison to the prior art.
An aspect of the invention can be regarded as a spindle motor for use in a disk drive. The spindle motor is provided with a spindle motor base. The spindle motor is further provided with a spindle motor hub rotatably attached to the spindle motor base. The spindle motor is further provided with a motor shaft in mechanical communication with the spindle motor base. The spindle motor is further provided with an inner ball bearing set surrounding the motor shaft. The inner ball bearing set has a first inner race and a first outer race. The first inner race is attached to the motor shaft. The spindle motor is further provided with an outer ball bearing set surrounding the inner ball bearing set. The outer ball bearing set has a second inner race and a second outer race. The second inner race is fixed relative to the first outer race.
Preferably, the inner and outer ball bearing sets are pre-loaded in compression. The first inner race may be axially off-set from the first outer race, and the second inner race may be axially off-set from the second outer race. The second inner race may be attached to the first outer race. Further, the outer ball bearing set may have a cross sectional size different than a cross sectional size of the inner ball bearing set.
In an embodiment of the present invention, the motor shaft is attached to the spindle motor hub. Thus, in this embodiment, the motor shaft is rotatable. The spindle motor hub has a hub annular member extending from the spindle motor hub, and the spindle motor hub is attached to the second outer race. The hub annular member is attached to the second outer race. The spindle motor base has a base annular member extending from the spindle motor base, and the base annular member is attached to the first outer race and the second inner race.
In another embodiment of the present invention, motor shaft is attached to the spindle motor base. Thus, in this embodiment, the motor shaft is stationary. The spindle motor base has a base annular member extending from the spindle motor, and the base annular member is attached to the second outer race. The spindle motor hub has a hub annular member extending from the spindle motor hub, and the hub annular member is attached to the first outer race and the second inner race.
In addition, according to another aspect of the present invention, there is provided a disk drive which includes a disk drive base and a spindle motor according to an above described embodiment. The spindle motor base attached to the disk drive base. The spindle motor base may be integrally formed with the disk drive base.